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Plasma Ghrelin Concentrations Are Decreased in Insulin-Resistant Obese Adults Relative to Equally Obese Insulin-Sensitive Controls

Division of Endocrinology (R.S.F., D.E.C.), University of Washington, Veterans Affairs Puget Sound Health Care System, Seattle, Washington 98108; and Stanford University School of Medicine (T.M., F.A., C.L.), Stanford, California 94305

Address all correspondence and requests for reprints to: Dr. David E. Cummings, University of Washington, Veterans Affairs Puget Sound Health Care System, 1660 South Columbian Way, S-111-Endo, Seattle, Washington 98108. E-mail: davidec{at}u.washington.edu.

	Abstract

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Ghrelin, an orexigenic hormone that may play a role in body weight regulation, is reduced in states of obesity. Because obesity is associated with insulin resistance and compensatory hyperinsulinemia, we determined whether these metabolic characteristics were independently associated with suppressed ghrelin concentrations. To investigate this hypothesis, using steady-state plasma glucose concentrations, we identified 20 insulin-resistant (IR) and 20 insulin-sensitive (IS) individuals who were equally obese. The mean body mass indexes were 32.5 ± 0.4 and 32.0 ± 0.4 kg/m² for the IR and IS groups, respectively. Fasting insulin concentrations were 19.5 and 7.4 µU/ml (P < 0.001), respectively. Ghrelin concentrations were suppressed in the IR group (252 ± 19 pg/ml) relative to the IS group (412 ± 35 pg/ml; P < 0.001). Ghrelin correlated inversely with both insulin resistance (r = –0.64; P < 0.001) and fasting insulin concentration (r = –0.58; P < 0.001). Multivariate analysis confirmed that both insulin resistance and hyperinsulinemia independently predicted low ghrelin concentrations. Our results demonstrate that in obese individuals, insulin resistance and hyperinsulinemia are inversely associated with ghrelin concentrations. Thus, insulin resistance or related metabolic abnormalities may constitute part of a feedback mechanism by which body weight is regulated in humans.

	Introduction

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GHRELIN, A PEPTIDE hormone secreted primarily by the stomach and small intestine, is the only known circulating orexigen (1, 2, 3, 4). Increasing evidence suggests that ghrelin plays a role in regulating premeal hunger and meal initiation as well as long-term energy balance (5, 6). For example, acute ghrelin injections potently stimulate appetite and food intake in multiple species, including humans (2, 3, 7, 8), and chronic administration increases body weight, not only by stimulating food intake, but also by decreasing energy expenditure and fat catabolism (2, 3, 7). In addition, blockade of ghrelin signaling using ghrelin receptor antagonists, antighrelin antibodies, or genetic techniques has been reported to decrease food intake and body weight (3, 9, 10, 11, 12). Finally, low body mass and weight loss are associated with elevations in ghrelin, whereas high body mass and weight gain are associated with decreased ghrelin concentrations (6, 13, 14, 15, 16, 17, 18). These observations suggest that ghrelin may serve as a signal to the brain of nutrient excess or depletion (6).

Despite the evidence favoring a role for ghrelin in long-term energy balance, it is unclear how a hormone secreted by the gastrointestinal tract can sense and respond to changes in body energy stores. This raises the possibility that a circulating adiposity signal, such as leptin or insulin, may regulate the production of ghrelin. Several lines of evidence suggest that leptin does not subserve this function (19). Insulin, a hormone that circulates in high concentrations in individuals who are insulin resistant, typically in the setting of obesity (20), is an attractive candidate for this signal. The changes in plasma insulin concentrations before and after meals are a virtual mirror image of fluctuations in ghrelin concentrations (5, 16). Additionally, short-term insulin infusions have been shown to decrease ghrelin concentrations in rodents (21) and humans (22, 23, 24, 25, 26), consistent with a possible causal role of insulin in suppressing ghrelin secretion.

The data implicating chronic hyperinsulinemia and/or insulin resistance in the negative regulation of ghrelin are suggestive, but inconsistent. For example, in a manner opposite that of ghrelin, insulin concentrations increase with increasing adiposity (20) and decrease with fasting (27) and weight loss (16). These findings raise the possibility that insulin is the mediator between body mass and ghrelin concentrations, and that hyperinsulinemia and/or insulin resistance, as signs of nutrient excess, suppress orexigenic ghrelin concentrations. Five published studies have evaluated this relationship (28, 29, 30, 31, 32). Results are conflicting, with some reports showing an inverse relationship between ghrelin and insulin concentrations or surrogate measures of insulin resistance, and others showing no association. It is important to note that conclusions from these investigations are limited by the fact that none included a physiological or precise measure of insulin resistance, relying instead on homeostatic model assessment (HOMA), which has been shown to be no more highly associated with insulin resistance than the fasting insulin concentration (33). Furthermore, the majority of published studies did not control for body mass, a major potential confounder between any observed association between ghrelin and insulin concentrations.

We clarified the relationships among insulin resistance, hyperinsulinemia, and ghrelin by evaluating 40 obese adults without concurrent medical diagnoses, who were matched for body mass index (BMI) and who were classified as either insulin resistant or insulin sensitive using a highly validated and precise physiological measure of insulin resistance, the steady-state plasma glucose test.

	Subjects and Methods

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Subjects

The study population consisted of 40 obese individuals who had responded to newspaper advertisements seeking healthy volunteers for a weight loss study. Potential participants were screened at Stanford University General Clinical Research Center, after giving written informed consent (protocol approved by the Stanford human subjects committee). To be eligible for this study, volunteers were required to be free of major medical illnesses, such as renal or hepatic disease, congestive heart failure, malignancy, or coronary artery disease; without history of eating disorders or change in weight within the past 4 wk; free of medications known to alter body weight or insulin resistance; and have a BMI between 29–35 kg/m².

Protocol

Volunteers meeting the above criteria and willing to be considered for further evaluation returned after an overnight fast for measurement of insulin-mediated glucose disposal (i.e. insulin sensitivity) by a modification (34) of the insulin suppression test as originally described (35). This test consists of a 180-min infusion with octreotide (0.27 µg/m²·min), insulin (25 mU/m²·min), and glucose (240 mg/m²·min). Blood is drawn at 10-min intervals from 150–180 min of the infusion to measure plasma glucose and insulin concentrations, and the mean of these four values is defined as the steady state plasma insulin or glucose (SSPG) concentration, respectively, for each individual. As steady state plasma insulin concentrations are similar for all subjects, the SSPG value provides a direct measure of the ability of insulin to mediate disposal of an infused glucose load; the higher the SSPG, the more insulin resistant the individual. Subjects were classified as insulin resistant if their SSPG value was 180 mg/dl or higher and as insulin sensitive if their SSPG was 120 mg/dl or less. These values represent the upper and lower 40th percentiles of SSPG concentrations, as measured in 490 healthy nondiabetic individuals (33). Of 100 screened individuals, 20 qualified as insulin sensitive. We then selected 20 insulin-resistant individuals matched to the insulin-sensitive subjects with respect to age, gender, and BMI. The characteristics of the two experimental groups are shown in Table 1. BMI was nearly identical in both groups: 32.0 ± 0.4 and 32.5 ± 0.4 (range, 29–35) kg/m² for the insulin-sensitive and -resistant groups, respectively. The only difference between the groups was the higher SSPG (by definition) concentration in the insulin-resistant group.

Glucose was measured as previously described (36). Samples were assayed for total immunoreactive ghrelin concentration with a modification of a commercial RIA (Phoenix Pharmaceuticals, Belmont, CA). This assay uses an ¹²⁵I-labeled ghrelin tracer and a rabbit polyclonal antibody against full-length, octanoylated human ghrelin that recognizes the acylated and des-acyl forms. Although only acylated ghrelin is bioactive (1), total ghrelin appears to be a reasonable surrogate for the acylated form because the ratio of the two levels is constant under a wide variety of conditions that affect ghrelin (10, 37). The lower and upper detection limits were 80 and 2500 pg/ml, and the intra- and interassay coefficients of variations were 5.4% and 9.2%, respectively. Insulin was measured via RIA as previously described (38). Although the study was not designed to evaluate the relationship between ghrelin and high density lipoprotein cholesterol (HDL-C), we included HDL-C (39) in our multivariate analyses because of a recent publication showing that HDL-C can bind to ghrelin (40) and therefore might influence measured ghrelin concentrations.

Statistical analyses

Data are expressed as the mean ± SEM. An unpaired t test was used to compare clinical and laboratory characteristics between insulin-sensitive and insulin-resistant individuals. ² analysis was used to compare categorical variables between the two groups. Multiple linear regression was performed to ascertain the independent effect of insulin resistance (as a categorical variable) on ghrelin after adjustment for BMI, age, and HDL-C. Because of colinearity, fasting plasma insulin was not included in the same regression model; it was analyzed in a separate model, with BMI, age, and HDL-C, to predict ghrelin concentrations. Due to unequal variances in the two groups, log-transformed values for insulin, SSPG, and ghrelin were used for correlations, and log-transformed ghrelin was used as the dependent variable in multivariate regression analysis. P < 0.05 was considered statistically significant. All analyses were performed using SAS 8.0 (SAS Institute, Inc., Cary, NC).

	Results

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The mean (±SEM) plasma ghrelin concentration was lower in the insulin-resistant group (252 ± 19 pg/ml) than in the insulin-sensitive group (412 ± 35 pg/ml; P < 0.001) despite equivalent body weight and BMI values in the two groups (Fig. 1A). The fasting insulin concentration was more than twice as high in the insulin-resistant group (19.5 ± 2.7 µU/ml) as in the insulin-sensitive group (7.4 ± 0.4 µU/ml; P < 0.001; Fig. 1B). Figure 2 displays the inverse relationship between log plasma ghrelin and log SSPG concentrations (r = –0.64; P < 0.001) as well as between log plasma ghrelin and log fasting plasma insulin concentrations (r = –0.58; P < 0.001). For ease of interpretation, the actual values are presented, but the correlation coefficients are for log-transformed SSPG, insulin, and ghrelin concentrations.

View larger version (20K): [in this window] [in a new window]   FIG. 1. Plasma ghrelin (A) and insulin (B) concentrations in insulin-resistant and insulin-sensitive obese individuals.

View larger version (20K): [in this window] [in a new window]   FIG. 2. Relationship between insulin resistance and ghrelin concentrations (A), and between fasting insulin and ghrelin concentrations (B). Insulin resistance was quantified via SSPG.

	Discussion

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The results of our study demonstrate that among obese, otherwise healthy adults with equivalent BMI values, plasma ghrelin concentrations are lower in those who are insulin resistant vs. those who are insulin sensitive. Because BMI was virtually identical in the two groups, our results help to clarify mixed observations in prior studies examining the relationships between ghrelin, obesity, and insulin resistance. Based on our findings, it appears that insulin resistance is independently and inversely associated with ghrelin concentration, with 41% of the variability in ghrelin attributable to insulin resistance. Adjustment, via multivariate analysis, for small degrees of variation among individual BMIs, confirmed that the inverse association between insulin resistance and ghrelin was significant and independent of BMI. Furthermore, multivariate analysis did not show any independent contribution of BMI to ghrelin concentrations.

These findings clarify and extend those of three prior studies (28, 29, 30) that demonstrated a significant inverse association between insulin resistance and ghrelin. As adiposity is correlated with both insulin resistance and ghrelin levels, it is important to eliminate confounding by obesity in the evaluation of the relationship between insulin resistance and ghrelin. Two of the prior studies (29, 30) did not control for adiposity, which, as expected, differed substantially according to the degree of insulin resistance. Thus, it is not possible in these studies to distinguish contributions of obesity vs. insulin resistance toward lowering of the ghrelin concentration. The third study (28) showed that among children with obesity resulting from melanocortin-4 receptor mutations, leptin deficiency, or Prader-Willi syndrome (PWS), insulin concentrations in the first two obese groups were significantly higher, and ghrelin concentrations were significantly lower than those in lean controls. The children with PWS, who were equally obese, had insulin concentrations less than half those in the other obese groups, and their ghrelin concentrations were more than twice as high, suggesting that insulin may play an independent role in modulating ghrelin concentrations. Indeed, multivariate analysis showed independent associations between both BMI and insulin with ghrelin in all but the PWS group.

In our study, BMI, which ranged from 29–35 kg/m², was not independently associated with ghrelin. This may indicate that the relationship between obesity and ghrelin is mediated via insulin resistance and/or compensatory hyperinsulinemia, and that adiposity per se does not affect ghrelin concentrations. Alternatively, our BMI range may have been too narrow and our sample size too small to identify a relationship between BMI and ghrelin. Thus, although our study cannot rule out a contribution of obesity to the regulation of ghrelin concentration, it demonstrates that ghrelin is not invariably suppressed in obese individuals, but, rather, is much more consistently suppressed among those obese individuals who are also insulin resistant.

It is important to note that virtually all prior studies on this topic used surrogate markers of insulin resistance that rely on fasting insulin concentrations, either alone or as a major component of indexes such as HOMA. The largest study (n = 490) validating HOMA as a measure of insulin resistance (measured by SSPG) showed that the correlation coefficient was 0.62, compared with a correlation coefficient of 0.61 for fasting insulin and insulin resistance, and a correlation coefficient of 0.98 for fasting insulin and HOMA (33). Thus, HOMA mainly reflects the hyperinsulinemia that accompanies insulin resistance and does not offer substantially more information regarding insulin resistance than does fasting insulin alone. This is particularly important in the study of obese individuals, in whom insulin concentrations may be elevated not only as a compensatory response to insulin resistance, but also due to decreased insulin clearance (41), rendering estimates of insulin resistance based on fasting insulin particularly subject to inaccuracies.

This may partially explain why two published studies found no association between insulin resistance, as measured by HOMA, and ghrelin. One, by Orio and colleagues (31), showed that although obese women with polycystic ovarian syndrome (PCOS) were more insulin resistant than obese non-PCOS controls, their ghrelin concentrations did not differ. Another, by Pagotto and colleagues (32), showed that although ghrelin concentrations were lower in obese PCOS subjects relative to obese non-PCOS controls, HOMA and fasting insulin were similar. Of note, the fasting insulin concentrations reported were similar (between groups) and relatively low in the Orio study (10 vs. 7 µU/ml) and were similar (between groups) and extremely high in the Pagotto study (21.3 vs. 21.5 µU/ml). As the two comparison groups in each of these studies had relatively similar insulin concentrations, it is possible that a more precise measure of insulin resistance might have demonstrated an association with ghrelin. Alternatively, Schofl et al. (30) found that in the "continuous infusion of glucose with model assessment" (CIGMA), which uses a 2-h glucose/insulin ratio in response to glucose infusion as an estimate of insulin sensitivity, increasing insulin sensitivity was independently predictive of ghrelin. Thus, the current analysis adds to prior findings by using a physiological and precise measure of insulin-mediated glucose disposal (insulin resistance) to identify two equally obese groups that are clearly different with respect to insulin resistance.

Despite the limitations of fasting insulin as a marker of insulin resistance, in our study the insulin-resistant group (as defined by SSPG concentration) was markedly hyperinsulinemic compared with the insulin-sensitive group. Thus, the group with low ghrelin concentrations had both insulin resistance and hyperinsulinemia compared to the group with higher ghrelin concentrations. In multivariate analysis, the insulin concentration was inversely associated with ghrelin, as was the SSPG concentration. As, in the nondiabetic population, insulin rises in response to insulin resistance, it is difficult in an observational study to separate the effects of these two variables with respect to ghrelin. Thus, our study cannot distinguish whether it is resistance to insulin, hyperinsulinemia, or an unmeasured associated factor that contributes to decreased ghrelin concentrations. We speculate that the control systems that regulate ghrelin levels are not subject to the mechanisms causing insulin resistance in major glucose-disposing tissues, such as muscle. Consequently, even in insulin-resistant individuals, these control systems may respond to excessive insulin signaling driven by compensatory hyperinsulinemia, thereby suppressing ghrelin concentrations. We hypothesize that the compensatory hyperinsulinemia associated with insulin resistance contributes directly to decreased ghrelin concentrations, and that the pathway by which insulin suppresses ghrelin is not resistant to insulin’s effect to the same degree as are muscle and liver. This hypothesis is consistent with studies showing that acute insulin infusions in animals or humans decrease ghrelin (21, 22, 23, 24, 25, 26), and that chemically induced insulin deficiency raises ghrelin concentrations (42). In a manner opposite to that of ghrelin, insulin concentrations rise both acutely in the postprandial state and chronically in the setting of insulin resistance, which is generally a manifestation of obesity. It is, therefore, reasonable to consider that insulin suppresses an orexigenic hormone as part of a complex feedback system that regulates appetite and body weight. In support of this hypothesis, it has been shown in four prospective studies that individuals with insulin concentrations in the highest quartile, compared with those with insulin concentrations in the lowest quartile, gain less weight over 5–14 yr (43, 44, 45, 46).

As our understanding of the endocrine functions of adipose tissue has expanded, various circulating hormones have been considered to play a role in body weight regulation and have thus been investigated with respect to ghrelin concentrations. Of these, leptin has received the most attention. Overall, however, extant evidence suggests that leptin is not an important regulator of ghrelin because 1) it correlates (inversely) weakly with ghrelin compared with other measures of adiposity; 2) it does not affect ghrelin when infused iv; and 3) in leptin-deficient or -resistant mice and humans who are obese, ghrelin concentrations are low, consistent with obesity, but inconsistent with the hypothetical inverse relationship between ghrelin and leptin (19). The same is true in the converse situation, in which lean animals with leptin overexpression (transgenics, central nervous system adenoviruses, or chronic leptin infusions) have high ghrelin concentrations, the opposite of that expected in the setting of high leptin concentrations, if leptin were to regulate ghrelin negatively (19). Although insulin appears to be a more likely candidate for ghrelin regulation, it is possible that there are unidentified circulating factors that are associated with both high insulin and low ghrelin concentrations; in which case, insulin is merely a marker of another regulatory factor.

Given the growing epidemic of obesity, it has become increasingly important to understand the complex physiological processes that regulate body weight. For this reason, much attention has recently centered on ghrelin, the only known circulating orexigen. Our finding that insulin resistance and compensatory hyperinsulinemia are independently associated with suppression of ghrelin furthers our understanding of the variable expression of ghrelin in humans. With continued research, it should be possible to elucidate exactly how the associations among insulin resistance, hyperinsulinemia, and ghrelin participate in the more intricate web of factors that regulate body weight.

	Footnotes

 
This work was supported by NIH Grants RR-000070-40, RR-16071-01, and R01-DK-61516.

Abbreviations: BMI, Body mass index; HDL-C, high density lipoprotein cholesterol; HOMA, homeostatic model assessment; IR, insulin resistant; PCOS, polycystic ovarian syndrome; PWS, Prader-Willi syndrome; SSPG, steady state plasma glucose.

Received September 29, 2003.

Accepted January 13, 2004.

	References

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1. Kojima M, Hosoda H, Date Y, Nakazato M, Matsuo H, Kangawa K 1999 Ghrelin is a growth-hormone-releasing acylated peptide from stomach. Nature 402:656–660[CrossRef][Medline]
2. Tschop M, Smiley DL, Helman ML 2000 Ghrelin induces adiposity in rodents. Nature 407:908–912[CrossRef][Medline]
3. Nakazato M, Murakami N, Date Y, Kojima M, Matsuo H, Kangawa K, Matsukura S 2001 A role for ghrelin in the central regulation of feeding. Nature 409:194–198[CrossRef][Medline]
4. Date Y, Kojima M, Hosoda H, Sawaguchi A, Mondal MS, Suganuma T, Matsukura S, Kangawa K, Nakazato M 2000 Ghrelin, a novel GH-releasing acylated peptide, is synthesized in a distinct endocrine cell type in the gastrointestinal tracts of rats and humans. Endocrinology 141:4255–4261[Abstract/Free Full Text]
5. Cummings DE, Purnell JQ, Frayo RS, Schmidova K, Wisse BE, Weigle DS 2001 A preprandial rise in plasma ghrelin levels suggests a role in meal initiation in humans. Diabetes 50:1714–1719[Abstract/Free Full Text]
6. Cummings DE, Shannon MH 2003 Roles for ghrelin in the regulation of appetite and body weight. Arch Surg 138:389[Free Full Text]
7. Asakawa A, Inui A, Kaga T, Yuzuriha H, Nagata T, Ueno N, Makino S, Fujimiya M, Niijima A, Fujino MA, Kasuga M 2001 Ghrelin is an appetite-stimulatory signal from stomach with structural resemblance to motilin. Gastroenterology 120:337–345[CrossRef][Medline]
8. Wren AM, Seal LJ, Cohen MA, Brynes AE, Frost GS, Murphy KG, Dhillo WS, Ghatei MA, Bloom SR 2001 Ghrelin enhances appetite and increases food intake in humans. J Clin Endocrinol Metab 86:5992–5995[Abstract/Free Full Text]
9. Shuto Y, Shibasaki T, Otagiri A, Kuriyama H, Ohata H, Tamura H, Kamegai J, Sugihara H, Oikawa S, Wakabayashi I 2002 Hypothalamic growth hormone secretagogue receptor regulates growth hormone secretion, feeding, and adiposity. J Clin Invest 109:1429–1436[CrossRef][Medline]
10. Murakami N, Hayashida T, Kuroiwa T, Nakahara K, Ida T, Mondal MS, Nakazato M, Kojima M, Kangawa K 2002 Role for central ghrelin in food intake and secretion profile of stomach ghrelin in rats. J Endocrinol 174:283[Abstract]
11. Bagnasco M, Tulipano G, Melis MR, Argiolas A, Cocchi D, Muller EE 2003 Endogenous ghrelin is an orexigenic peptide acting in the arcuate nucleus in response to fasting. Regul Pept 111:161–167[CrossRef][Medline]
12. Asakawa A, Inui A, Kaga T, Katsuura G, Fujimiya M, Fujino MA, Kasuga M 2003 Antagonism of ghrelin receptor reduces food intake and body weight gain in mice. Gut 52:947–952[Abstract/Free Full Text]
13. Tschop M, Weyer C, Tataranni PA, Devanarayan V, Ravussin E, Heiman ML 2001 Circulating ghrelin levels are decreased in human obesity. Diabetes 50:707–709[Abstract/Free Full Text]
14. Shiiya T, Nakazato M, Mizuta M, Date Y, Mondal MS, Tanaka M, Nozoe S, Hosoda H, Kangawa K, Matsukura S 2002 Plasma ghrelin levels in lean and obese humans and the effect of glucose on ghrelin secretion. J Clin Endocrinol Metab 87:240–244[Abstract/Free Full Text]
15. Cummings DE, Clement K, Purnell JQ, Vaisse C, Foster KE, Frayo RS, Schwartz MW, Basdevant A, Weigle DS 2002 Elevated plasma ghrelin levels in Prader Willi syndrome. Nat Med 8:643–644[CrossRef][Medline]
16. Cummings DE, Weigle DS, Frayo RS, Breen PA, Ma MK, Dellinger EP, Purnell JQ 2002 Plasma ghrelin levels after diet-induced weight loss or gastric bypass surgery. N Engl J Med 346:1623–1630[Abstract/Free Full Text]
17. Hansen TK, Dall R, Hosoda H, Kojima M, Kangawa K, Christiansen JS, Jorgensen JO 2002 Weight loss increases circulating levels of ghrelin in human obesity. Clin Endocrinol 56:203–206[CrossRef][Medline]
18. Otto B, Cuntz U, Fruehauf E, Wawarta R, Folwaczny C, Riepl RL, Heiman ML, Lehnert P, Fichter M, Tschop M 2001 Weight gain decreases elevated plasma ghrelin concentrations of patients with anorexia nervosa. Eur J Endocrinol 145:669–673[Abstract]
19. Cummings DE, Foster KE 2003 Ghrelin-leptin tango in body-weight regulation. Gastroenterology 124:1532–1535[CrossRef][Medline]
20. Abbasi F, Brown BW, Lamendola C, McLaughlin T, Reaven GM 2002 Relationship between obesity, insulin resistance, and coronary heart disease risk. J Am Coll Cardiol 40:937–943[Abstract/Free Full Text]
21. McCowen KC, Maykel JA, Bistrian BR, Ling PR 2002 Circulating ghrelin concentrations are lowered by intravenous glucose or hyperinsulinemic euglycemic conditions in rodents. J Endocrinology 175:R7–R11
22. Saad MF, Bernaba B, Hwu C, Jinagouda S, Fahmi S, Kogosov E, Boyadjian R 2002 Insulin regulates plasma ghrelin concentration. J Clin Endocrinol Metab 87:3997–4000[Abstract/Free Full Text]
23. Mohlig M, Spranger J, Otto B, Ristow M, Tschop M, Pfeiffer AF 2002 Euglycemic hyperinsulinemia, but not lipid infusion, decreases circulating ghrelin levels in humans. J Endocrinol Invest 25:RC36–RC38
24. Lucidi P, Murdolo G, Loreto C, DeCicco A, Parlanti N, Fanelli C, Santeusanio F, Bolli G, DeFeo P 2002 Ghrelin is not necessary for adequate hormonal counterregulation of insulin-induces hypoglycemia. Diabetes 51:2911–2914[Abstract/Free Full Text]
25. Flanagan DE, Evans ML, Monsod TP, Rife F, Heptulla RA, Tamborlane WV, Sherwin RS 2003 The influence of insulin on circulating ghrelin. Am J Physiol 284:E313–E316
26. Anderwald C, Brabant G, Bernroider E, Horn R, Bhrem A, Waldhausl W, Roden M 2003 Insulin-dependent modulation of plasma ghrelin and leptin concentrations is less pronounced in type 2 diabetic patients. Diabetes 52:1792–1798[Abstract/Free Full Text]
27. Flakoll P, Carlson G, Cherrington A 1996 Physiologic action of insulin. In: LeRoith D, Taylor SI, Olefsky JM, eds. Diabetes mellitus. Philadelphia: Lippincott-Raven; 121–132
28. Haqq AM, Farooqi S, O’Rahilly S, Stadler DD, Rosenfeld RG, Pratt KL, LaFranchi SH, Purnell JQ 2003 Serum ghrelin levels are inversely correlated with body mass index, age, and insulin concentrations in normal children and are markedly increased in Prader-Willi syndrome. J Clin Endocrinol Metab 88:174–178[Abstract/Free Full Text]
29. Ikezaki A, Hosoda H, Ito K, Iwama S, Miura N, Matsuoka H, Kondo C, Kojima M, Kangawa K, Sugihara S 2002 Fasting plasma ghrelin levels are negatively correlated with insulin resistance and PAI-1, but not with leptin, in obese children and adolescents. Diabetes 51:3408–3411[Abstract/Free Full Text]
30. Schofl C, Horn R, Schill T, Schlosser HW, Muller MJ, Brabant G 2002 Circulating ghrelin levels in patients with polycystic ovary syndrome. J Clin Endocrinol Metab 87:4607–4610[Abstract/Free Full Text]
31. Orio F, Lucidi P, Palomba S, Tauchmanova L, Cascella T, Russo T, Zullo F, Colao A, Lombardi G, De Feo P 2003 Circulating ghrelin concentrations in the polycystic ovary syndrome. J Clin Endocrinol Metab 88:943–945
32. Pagotto U, Gambineri A, Vicennati V, Heiman ML, Tschop M, Pasquali R 2002 Plasma ghrelin, obesity, and the polycystic ovary syndrome: correlation with insulin resistance and androgen levels. J Clin Endocrinol Metab 87:5625–5629[Abstract/Free Full Text]
33. Yeni-Komshian H, Caratoni M, Abbasi F, Reaven GM 2000 Relationship between several surrogate estimates of insulin resistance and quantification of insulin-mediated glucose disposal in 490 healthy, nondiabetic volunteers. Diabetes Care 23:171–175[Abstract]
34. Pei D, Jones CN, Bhargava R, Chen YD, Reaven GM 1994 Evaluation of octreotide to assess insulin-mediated glucose disposal by the insulin suppression test. Diabetologia 37:843–845[CrossRef][Medline]
35. Shen SW, Reaven GM, Farquhar JW 1970 Comparison of impedance to insulin-mediated glucose uptake in normal and diabetic subjects. J Clin Invest 49:2151–2160
36. Kadish AK, Little RL, Sternberg JC 1963 A new and rapid method for determination of glucose by measurement of rate of oxygen consumption. Clin Chem 88:137–146
37. Ariyasu H, Takaya K, Hosoda H, Iwakura H, Ebihara K, Mori K, Ogawa Y, Hosoda K, Akamizu T, Kojima M, Kangawa K, Nakao K 2002 Delayed short-term secretory regulation of ghrelin in obese animals: evidenced by a specific RIA for the active form of ghrelin. Endocrinology 143:3341–3350[Abstract/Free Full Text]
38. Hales CN, Randle PJ 1963 Immunoassay of insulin and insulin-antibody precipitate. Biochem J 88:137–146[Medline]
39. Havel RJ, Eder HA, Bragdon JH 1955 The distribution of ultracentrifugally separated lipoproteins in human serum. J Clin Invest 34:1345–1353
40. Beaumont NJ, Skinner VO, Tan TMM, Ramesh BS, Byrne DJ, MacColl GS, Keen JN, Bouloux PM, Mikhailidis DP, Bruckdorfer KR, Vanderpump MP, Srai KS 2003 Ghrelin can bind to a species of high density lipoprotein associated with paraoxonase. J Biol Chemistry 278:8877–8880[Abstract/Free Full Text]
41. Jones CNO, Abbasi F, Caratoni M, Polonsky KS, Reaven GM 2000 Roles of insulin resistance and obesity in regulation of plasma insulin concentrations. Am J Physiol 278:E501–E508
42. Masaoka T, Suzuki H, Hosoda H, Ota T, Minegishi Y, Nagata H, Kangawa K, Ishii H 2003 Enhanced plasma ghrelin levels in rats with streptozotocin-induced diabetes. FEBS Lett 541:64–68[CrossRef][Medline]
43. Swinburn BA, Nyomba BL, Saad MF, Zurlo F, Raz I, Knowler WC, Lillioja S, Bogardus C, Ravussin E 1991 Insulin resistance associated with lower rates of weight gain in Pima Indians. J Clin Invest 88:168–173
44. Hoag S, Marshall JA, Jones RH, Hamman RF 1995 High fasting insulin levels associated with lower rates of weight gain inpersons with normal glucose tolerance: the San Luis Valley Diabetes Study. Int J Obesity 19:175–180[Medline]
45. Schwartz MW, Boyko EJ, Kahn SE, Ravussin E, Bogardus C 1995 Reduced insulin secretion: an independent predictor of body weight gain. J Clin Endocrinol Metab 80:1571–1576[Abstract/Free Full Text]
46. Valdez R, Mitchell BD, Haffner SM, Hazuda HP, Morales PA, Monterrosa A, Stern MP 1994 Predictors of weight change in a bi-ethnic population: the San Antonio Heart Study. Int J Obesity 18:85–91

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				A. Geliebter, C. N. Ochner, and R. Aviram-Friedman Appetite-Related Gut Peptides in Obesity and Binge Eating Disorder American Journal of Lifestyle Medicine, July 1, 2008; 2(4): 305 - 314. [Abstract] [PDF]

				E. Feigerlova, G. Diene, F. Conte-Auriol, C. Molinas, I. Gennero, J.-P. Salles, C. Arnaud, and M. Tauber Hyperghrelinemia Precedes Obesity in Prader-Willi Syndrome J. Clin. Endocrinol. Metab., July 1, 2008; 93(7): 2800 - 2805. [Abstract] [Full Text] [PDF]

				K. E. Foster-Schubert, J. Overduin, C. E. Prudom, J. Liu, H. S. Callahan, B. D. Gaylinn, M. O. Thorner, and D. E. Cummings Acyl and Total Ghrelin Are Suppressed Strongly by Ingested Proteins, Weakly by Lipids, and Biphasically by Carbohydrates J. Clin. Endocrinol. Metab., May 1, 2008; 93(5): 1971 - 1979. [Abstract] [Full Text] [PDF]

				U. Mager, M. Kolehmainen, V. D F de Mello, U. Schwab, D. E Laaksonen, R. Rauramaa, H. Gylling, M. Atalay, L. Pulkkinen, and M. Uusitupa Expression of ghrelin gene in peripheral blood mononuclear cells and plasma ghrelin concentrations in patients with metabolic syndrome. Eur. J. Endocrinol., April 1, 2008; 158(4): 499 - 510. [Abstract] [Full Text] [PDF]

				E. T. Vestergaard, N. H. Andersen, T. K. Hansen, L. M. Rasmussen, N. Moller, K. E. Sorensen, E. Sloth, and J. O. L. Jorgensen Cardiovascular effects of intravenous ghrelin infusion in healthy young men Am J Physiol Heart Circ Physiol, November 1, 2007; 293(5): H3020 - H3026. [Abstract] [Full Text] [PDF]

				R. Barazzoni, M. Zanetti, C. Ferreira, P. Vinci, A. Pirulli, M. Mucci, F. Dore, M. Fonda, B. Ciocchi, L. Cattin, et al. Relationships between Desacylated and Acylated Ghrelin and Insulin Sensitivity in the Metabolic Syndrome J. Clin. Endocrinol. Metab., October 1, 2007; 92(10): 3935 - 3940. [Abstract] [Full Text] [PDF]

				M. R. Hayes, C. K. Miller, J. S. Ulbrecht, J. L. Mauger, L. Parker-Klees, M. D. Gutschall, D. C. Mitchell, H. Smiciklas-Wright, and M. Covasa A Carbohydrate-Restricted Diet Alters Gut Peptides and Adiposity Signals in Men and Women with Metabolic Syndrome J. Nutr., August 1, 2007; 137(8): 1944 - 1950. [Abstract] [Full Text] [PDF]

				W. H. Park, Y. J. Oh, G. Y. Kim, S. E. Kim, K.-H. Paik, S. J. Han, A. H. Kim, S. H. Chu, E. K. Kwon, S. W. Kim, et al. Obestatin Is Not Elevated or Correlated with Insulin in Children with Prader-Willi Syndrome J. Clin. Endocrinol. Metab., January 1, 2007; 92(1): 229 - 234. [Abstract] [Full Text] [PDF]

				D. H. St-Pierre, A. D. Karelis, L. Coderre, F. Malita, J. Fontaine, D. Mignault, M. Brochu, J.-P. Bastard, K. Cianflone, E. Doucet, et al. Association of Acylated and Nonacylated Ghrelin with Insulin Sensitivity in Overweight and Obese Postmenopausal Women J. Clin. Endocrinol. Metab., January 1, 2007; 92(1): 264 - 269. [Abstract] [Full Text] [PDF]

				P. Marzullo, A. Caumo, G. Savia, B. Verti, G. E. Walker, S. Maestrini, A. Tagliaferri, A. M. Di Blasio, and A. Liuzzi Predictors of Postabsorptive Ghrelin Secretion after Intake of Different Macronutrients J. Clin. Endocrinol. Metab., October 1, 2006; 91(10): 4124 - 4130. [Abstract] [Full Text] [PDF]

				F. Bacha and S. A. Arslanian Ghrelin and Peptide YY in Youth: Are There Race-Related Differences? J. Clin. Endocrinol. Metab., August 1, 2006; 91(8): 3117 - 3122. [Abstract] [Full Text] [PDF]

				G. Mingrone, L. Granato, E. Valera-Mora, A. Iaconelli, M. F Calvani, R. Bracaglia, M. Manco, G. Nanni, and M. Castagneto Ultradian ghrelin pulsatility is disrupted in morbidly obese subjects after weight loss induced by malabsorptive bariatric surgery Am. J. Clinical Nutrition, May 1, 2006; 83(5): 1017 - 1024. [Abstract] [Full Text] [PDF]

				K. H. Paik, Y. H. Choe, W. H. Park, Y. J. Oh, A. H. Kim, S. H. Chu, S. W. Kim, E. K. Kwon, S. J. Han, W. Y. Shon, et al. Suppression of Acylated Ghrelin during Oral Glucose Tolerance Test Is Correlated with Whole-Body Insulin Sensitivity in Children with Prader-Willi Syndrome J. Clin. Endocrinol. Metab., May 1, 2006; 91(5): 1876 - 1881. [Abstract] [Full Text] [PDF]

				Y. L. Pagan, S. S. Srouji, Y. Jimenez, A. Emerson, S. Gill, and J. E. Hall Inverse Relationship between Luteinizing Hormone and Body Mass Index in Polycystic Ovarian Syndrome: Investigation of Hypothalamic and Pituitary Contributions J. Clin. Endocrinol. Metab., April 1, 2006; 91(4): 1309 - 1316. [Abstract] [Full Text] [PDF]

				M. Romon, S. Gomila, P. Hincker, B. Soudan, and J. Dallongeville Influence of Weight Loss on Plasma Ghrelin Responses to High-Fat and High-Carbohydrate Test Meals in Obese Women J. Clin. Endocrinol. Metab., March 1, 2006; 91(3): 1034 - 1041. [Abstract] [Full Text] [PDF]

				S. C. Griffen, K. Oostema, K. L. Stanhope, J. Graham, D. M. Styne, N. Glaser, D. E. Cummings, M. H. Connors, and P. J. Havel Administration of Lispro Insulin with Meals Improves Glycemic Control, Increases Circulating Leptin, and Suppresses Ghrelin, Compared with Regular/NPH Insulin in Female Patients with Type 1 Diabetes J. Clin. Endocrinol. Metab., February 1, 2006; 91(2): 485 - 491. [Abstract] [Full Text] [PDF]

				K. Teff Learning Hunger: Conditioned Anticipatory Ghrelin Responses in Energy Homeostasis Endocrinology, January 1, 2006; 147(1): 20 - 22. [Full Text] [PDF]

				C. Langenberg, J. Bergstrom, G. A. Laughlin, and E. Barrett-Connor Ghrelin and the Metabolic Syndrome in Older Adults J. Clin. Endocrinol. Metab., December 1, 2005; 90(12): 6448 - 6453. [Abstract] [Full Text] [PDF]

				M. Tesauro, F. Schinzari, M. Iantorno, S. Rizza, D. Melina, D. Lauro, and C. Cardillo Ghrelin Improves Endothelial Function in Patients With Metabolic Syndrome Circulation, November 8, 2005; 112(19): 2986 - 2992. [Abstract] [Full Text] [PDF]

				R. Giordano, A. Picu, U. Pagotto, R. De Iasio, L. Bonelli, F. Prodam, F. Broglio, L. Marafetti, R. Pasquali, M. Maccario, et al. The negative association between total ghrelin levels, body mass and insulin secretion is lost in hypercortisolemic patients with Cushing's disease Eur. J. Endocrinol., October 1, 2005; 153(4): 535 - 543. [Abstract] [Full Text] [PDF]

				L. J. Moran, N. D. Luscombe-Marsh, M. Noakes, G. A. Wittert, J. B. Keogh, and P. M. Clifton The Satiating Effect of Dietary Protein Is Unrelated to Postprandial Ghrelin Secretion J. Clin. Endocrinol. Metab., September 1, 2005; 90(9): 5205 - 5211. [Abstract] [Full Text] [PDF]

				O. Gimenez-Palop, G. Gimenez-Perez, D. Mauricio, E. Berlanga, N. Potau, C. Vilardell, J. Arroyo, J.-M. Gonzalez-Clemente, and A. Caixas Circulating ghrelin in thyroid dysfunction is related to insulin resistance and not to hunger, food intake or anthropometric changes Eur. J. Endocrinol., July 1, 2005; 153(1): 73 - 79. [Abstract] [Full Text] [PDF]

				A. P. Goldstone, M. Patterson, N. Kalingag, M. A. Ghatei, A. E. Brynes, S. R. Bloom, A. B. Grossman, and M. Korbonits Fasting and Postprandial Hyperghrelinemia in Prader-Willi Syndrome Is Partially Explained by Hypoinsulinemia, and Is Not Due to Peptide YY3-36 Deficiency or Seen in Hypothalamic Obesity Due to Craniopharyngioma J. Clin. Endocrinol. Metab., May 1, 2005; 90(5): 2681 - 2690. [Abstract] [Full Text] [PDF]

				E. Kellokoski, S. M. Poykko, A. H. Karjalainen, O. Ukkola, J. Heikkinen, Y. A. Kesaniemi, and S. Horkko Estrogen Replacement Therapy Increases Plasma Ghrelin Levels J. Clin. Endocrinol. Metab., May 1, 2005; 90(5): 2954 - 2963. [Abstract] [Full Text] [PDF]